These Challenge Grifo are beautiful clinchers. Note that Challenge call them Open Tubulars meaning they're made like their tubulars before fitting a clincher style bead. Extremely high TPI, so very supple. Since they're made of cotton, it is advisable to seal the tyre walls. I've done an experiment here, top one is sealed in Pritt Copydex (latex base solvent free glue). It had nil effect to the feel of the tyre.
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